The invention relates to a process for telomerizing noncyclic olefins having at least two conjugated double bonds, in particular to the preparation of 1-octa-2,7-dienyl derivatives, by reacting a 1,3-butadiene-containing hydrocarbon mixture, in particular crack C4, with nucleophiles.
The telomerization products which are formed from two moles of 1,3-butadiene and one mole of nucleophile (unsaturated amines, unsaturated alcohols and their esters and ethers) are starting materials for organic syntheses. The oxygen-containing derivatives are precursors for the preparation of linear C8-alcohols and C8-olefins, in particular 1-octanol and 1-octene. 1-Octanol in turn is used, for example, to obtain plasticizers. 1-Octene is a valuable comonomer for the modification of polyethylene and polypropylene.
The telomerization of butadiene with a nucleophile to give octadienyl derivatives is catalyzed by metal complexes, in particular palladium compounds.
Examples of telomerization reactions are described, inter alia, in E. J, Smutny, J. Am. Chem. Soc. 1967, 89, 6793; S. Takahashi, T. Shibano, N. Hagihara, Tetrahedron Lett. 1967, 2451; EP-A-0 561 779, U.S. Pat. Nos. 3,499,042, 3,530,187, GB 1 178 812, NL 6 816 008, GB 1 248 593, U.S. Pat. Nos. 3,670,029, 3,670,032, 3,769,352, 3,887,627, GB 1 354 507, DE 20 40 708, U.S. Pat. Nos. 4,142,060, 4,146,738, 4,196,135, GB 1 535 718, U.S. Pat. No. 4,104,471, DE 21 61 750 and EP-A-0 218 100.
The feedstocks used for the preparation of octadienyl derivatives may be pure 1,3-butadiene or 1,3-butadiene-containing hydrocarbon mixtures, for example crack C4.
Owing to the costly and inconvenient removal process, 1,3-butadiene is a relatively expensive feedstock. It is therefore usually more economically viable to select 1,3-butadiene-containing hydrocarbon mixtures as the feedstock for the telomerization. This is possible since most of the accompanying substances, such as saturated hydrocarbons, for example n-butane or isobutane, or monoolefins, for example isobutene and linear butenes, behave inertly in the telomerization reaction. Only inhibitors, i.e. substances which reduce the space-time yield or the selectivity or increase the catalytic consumption, should be removed beforehand.
According to DE 195 23 335, it is advisable, when using the C4 fraction from naphtha crackers as the 1,3-butadiene-containing raw material, to limit the concentration of acetylenic compounds and of allenes in the reactant for the telomerization. The sum of acetylenically and allenically unsaturated compounds should not exceed 1% by mass based on 1,3-butadiene. For the removal of these troublesome components, reference is made to known processes without mentioning or citing particular processes.
With reference to this patent (DE 195 23 335), DE 101 49 348, DE 102 29 290 and DE 103 29 042 indicate, without specifying concentration limits, that it is favorable to remove acetylenic and allenic compounds before the telomerization.
WO 91/09822 states that it is appropriate to remove acetylenically unsaturated compounds by selective hydrogenation from the C4 mixture obtained in the cracking process of naphtha, gas oil or LPG. The hydrogenation process used is not disclosed. In the examples, a raw material having a total content of acetylenes below 60 ppm is used and does not contain any specified content of allenes.
The acetylenic compounds can be removed by extraction or hydrogenation of these compounds. In the removal of the acetylenic compounds (methylacetylene (propyne), ethylacetylene (butyne), vinylacetylene (butenyne)) by hydrogenation, processes are employed in which the acetylenic compounds are hydrogenated with high selectivity, substantially without hydrogenation of 1,3-butadiene and monoolefins. The catalysts used are hydrogenation catalysts which comprise copper, copper in combination with base metals, copper in combination with noble metals or metal catalysts of metals of transition group VIII of the Periodic Table of the Elements, for example palladium catalysts. Corresponding processes are described, inter alia, in the following patents: U.S. Pat. Nos. 6,576,588, 6,417,419, 6,225,515, 6,015,933, 6,194,626, 6,040,489, 4,493,906, 4,440,956, 4,101,451, 3,912,789, 3,751,508, 3,541,178, 3,327,013, 3,218,268, EP 1 217 060, EP 1 151 790, EP1 070 695, EP 0 273 900, NL 6 613 942.
The removal of allenes, especially of 1,2-butadiene, by hydrogenation is substantially more difficult than the selective removal of acetylenic compounds. The reactivity of 1,2-butadiene in the hydrogenation is only slightly higher than that of 1,3-butadiene. Therefore, 1.3 butadiene losses are unavoidable in the removal of 1,2-butadiene from 1,3-butadiene-containing hydrocarbon mixtures by hydrogenation.
For example, WO 98/12160 details a process for simultaneously removing acetylenic compounds and 1,2-butadiene from a 1,3-butadiene-containing hydrocarbon stream by hydrogenation over a palladium catalyst in a reactive distillation column. Although the content of acetylenic compounds in the top product had only been reduced by approx. 60% and that of 1,2-butadiene only by 32% in the example 1 reported there, as much as 3% of the 1,3-butadiene had been lost by hydrogenation.
In Angew. Chem. 2005, 117, 2062-2065, Jeroen W. Sprengers et al. report that Pd complex catalysts which have N-heterocyclic ligands as ligands are suitable as catalysts for hydrogenation, in particular for the hydrogenation of 1-phenyl-1-propyne to 1-phenyl-1-propene and 1-phenyl-1-propane.
In the preparation of 2,7-octadienyl derivatives from crack C4 by telomerization according to the prior art, complicated processes, especially with regard to the apparatus complexity, are needed to remove inhibitors such as alkynes from the feedstock mixture. These processes have the disadvantage that a portion of the 1,3-butadiene, especially when it is attempted to get the alkyne content in the feedstock mixture below the detection limit, is lost in the removal of the inhibitors. When 1,3-butadiene losses are avoided by dispensing with a substantially full removal of the inhibitors, a lower space-time yield or selectivity in the telomerization or a higher catalyst consumption has to be accepted.